The present invention relates to a transparent layered product including a glass sheet and a coating film with a rough surface and a glass article using the same (for example, a photoelectric conversion device, a multiple-glazing unit, or the like).
A transparent layered product in which a thin film such as a tin oxide film or the like is formed on a glass sheet has been used widely for a thin film photoelectric conversion device (a thin film solar cell), heat-reflecting glass, or the like. For example, JP 7-29402 B describes heat-reflecting glass formed by stacking a silicon film, a silicon oxide film, and a tin oxide film on a glass sheet in this order.
Tin oxide in a film formed by pyrolysis on a high-temperature substrate becomes a polycrystalline film. The polycrystalline product of tin oxide has a surface with roughness caused by the growth of crystal grains according to the increase in film thickness. In a thin film photoelectric conversion device, the surface roughness of a tin oxide film as a transparent electrode enables photovoltaic characteristics to be improved due to a light trapping effect.
For example, JP 61-288473 A discloses a thin film photoelectric conversion device including a tin oxide film having a rough surface including convex portions with heights in the range between 100 and 500 nm and intervals between respective convex portions in the range between 200 and 1000 nm. The rough surface is formed by etching after film formation.
Further, JP 2-503615 A discloses a substrate for a thin film photoelectric conversion device including a tin oxide film having a surface provided with convex portions with diameters in the range between 0.1 and 0.3 xcexcm and the ratio of height/diameter in the range between 0.7 and 1.2. In addition, JP 2-503615 A also discloses a chemical vapor deposition method (a CVD method) using a mixed gas containing tin tetrachloride, water vapor, methyl alcohol, nitrogen and the like, which is carried out on a precut glass sheet, as a method of manufacturing a tin oxide film.
JP 4-133360 A discloses a substrate for a thin film photoelectric conversion device including a tin oxide film having a surface with pyramidal convex portions with heights in the range between 100 and 300 nm and angles with respect to the normal line of the principal plane of the substrate in the range between 30xc2x0 and 60xc2x0. Similarly, JP 4-133360 A also discloses a CVD method using a mixed gas containing tin tetrachloride, oxygen, nitrogen and the like, which is carried out on a glass sheet with a temperature in the range between 350 and 500xc2x0 C., as a method of manufacturing a tin oxide film.
Besides the tin oxide film, coating films formed of zinc oxide, ITO (indium tin oxide), titanium oxide, silicon oxide or the like also are formed on a glass sheet to add various functions. These coating films are formed on a glass sheet as, for example, a reflection-suppression film, an electromagnetic shielding film, an antifouling film, a low-emissivity film (Low-E film), or as a component thereof, in addition to a transparent conductive film and a heat reflecting film.
As described above, when a transparent layered product is obtained by forming a crystalline or amorphous coating film for adding various functions to a glass sheet, the light reflectance may be higher than that required in some cases. In addition, for example, when the transparent layered product is used as a substrate for a photoelectric conversion device or reflection-suppression glass, a lower reflectance is preferable. Depending on the intended use, the coloring of reflected light due to the formation of the coating film may be intended to be suppressed to a degree causing no harm to the desired appearance in some cases.
Judging from the fact that a porous surface has a refractive index distribution in the depth direction, it is conceivable that a transition layer in which the refractive index varies continuously is present at the surface of a coating film such as a tin oxide film or the like. This transition layer can affect reflected light from the transparent layered product. Conventionally, particularly in the field of photoelectric conversion devices, the heights and intervals of convex portions of the rough surface of a tin oxide film have been adjusted. Conventionally, however, attention merely has been paid to the physical shape and size of convex or concave portions of the rough surface. The refractive index distribution in the transition layer produced at the surface of a coating film does not depend only on the shape and size of the individual convex or concave portions of the rough surface but also is affected by the distribution of them. Therefore, the refractive index distribution in the transition layer should not be evaluated based on observation of the rough surface in a very limited region by an electron microscope and is required to be evaluated based on optical measurement.
It is an object of the present invention that in a transparent layered product including a glass sheet and a coating film exhibiting various functions, the reflectance of light entering the transparent layered product is decreased by suitably controlling the refractive index distribution in a transition layer at the surface of the coating film. Further, another object of the present invention is to provide a glass article using this transparent layered product, particularly a multiple-glazing unit and a photoelectric conversion device such as a photovoltaic device.
The present inventors found that surprisingly, the aforementioned objects were able to be achieved by controlling the pattern of the variation in refractive index in a thickness direction in a transition layer present at the surface of the coating film.
The transparent layered product of the present invention includes a glass sheet and a coating film having a surface with roughness, which is formed on the glass sheet, and a transition layer in which the refractive index varies continuously in its thickness direction is present at the surface of the coating film. The variation in refractive index in the transition layer is indicated by a convex curve over the whole region of the transition layer, when the variation is shown on a plane defined by a horizontal axis indicating the refractive index and a vertical axis indicating the thickness direction of the transition layer, with the glass sheet positioned on a lower side.
When the coating film is formed as an outermost layer, the refractive index in the transition layer varies continuously in its thickness direction to approach the refractive index of air (1) from the refractive index of the coating film, in the direction of the outside air. On the other hand, when another thin film is further formed on the coating film having a surface with roughness, the refractive index in the transition layer approaches the refractive index of the another thin film while varying continuously in its thickness direction. In this case, it is preferable that the refractive index varies continuously from a refractive index n1 of the coating film to a refractive index n2 of the thin film formed thereon so that the variation in refractive index is indicated by a convex locus (curve) over the whole region when being shown on a plane. The magnitude correlation between the refractive index n1 and the refractive index n2 is not particularly limited.
In the transparent layered product, it is preferable that the coating film is a crystalline coating film. It also is preferable that the roughness is caused by crystal grains in the crystalline coating film. In this connection, the crystalline coating film may contain amorphous portions regionally, and a film with a crystalline fraction in volume of at least 50% as a whole is taken as corresponding to a xe2x80x9ccrystallinexe2x80x9d film.
In the transparent layered product, it is preferable that the crystalline coating film contains, as a main component, at least one selected from tin oxide, zinc oxide, indium oxide, and titanium oxide. Particularly, a coating film containing tin oxide as the main component is useful for many purposes. In this specification, the xe2x80x9cmain componentxe2x80x9d denotes a component accounting for at least 50 wt.% of the whole amount.
In the transparent layered product, it is preferable that the coating film is formed on an undercoating film on the glass sheet. In this case, it is further preferable that the undercoating film is a coating film formed by pyrolysis of a material containing halogen, and the coating film has a surface with roughness caused by production of or loss after the production of compound grains of an alkaline component in the glass sheet and the halogen. Utilization of the roughness enables a transition layer having the above-mentioned refractive index distribution to be obtained easily.
In the transparent layered product, the roughness caused by a reaction product of the alkaline component in the glass may be utilized directly. In other words, in the transparent layered product of the present invention, the coating film having a surface with roughness may be a coating film formed by pyrolysis of a material containing halogen, and the coating film formed by pyrolysis may have a surface with roughness caused by production of or loss after the production of compound grains of an alkaline component in the glass sheet and the halogen. Particularly, when such production of compound grains is utilized, the coating film having a surface with roughness is not required to be a crystalline coating film.
In the transparent layered product, it is preferable that the thickness of the transition layer in the coating film corresponds to 30% or lower of the thickness of a layer having a substantially constant refractive index in the coating film. The thickness of the transition layer is not particularly limited, but preferably corresponds to at least 10% of the thickness of the layer having a substantially constant refractive index in the coating film.
In the transparent layered product, the coating film having a surface with roughness may be an insulating coating film, but a conductive coating film (a transparent conductive film) is used in a photoelectric conversion device or the like.
The transparent layered product can be used for various purposes. For example, it can be used as reflection-suppression (anti-reflection) glass, electromagnetic shielding glass, glass to be electrified for preventing fogging or the like, antifouling glass, antistatic glass, low-emissivity glass (Low-E glass), glass for information display equipment (for instance, a touch control panel), or glass for a top plate of a duplicator.
The transparent layered product may be used as a glass article by being combined with other members. For example, the present invention includes a multiple-glazing unit in which at least two transparent substrates are positioned to face each other via at least one inner layer selected from a group consisting of an air layer, an inert gas layer, and a low pressure layer and at least one of the transparent substrates is the transparent layered product. Furthermore, the multiple-glazing unit may be used for a door of a refrigerator (a refrigerated display case), and the conductive coating film (a coating film having a surface with roughness) included in the multiple-glazing unit is used as a heating element. In this case, the refrigerator is provided with an electrification device for passing a current in the conductive coating film.
In addition, for example, when the transparent layered product of the present invention is used in information display equipment, this information display equipment displays information through the transparent layered product. This information display equipment is provided with a display device for displaying information and the conductive film included in the transparent layered product serves as a transparent electrode. Furthermore, for instance, when the transparent layered product of the present invention is used in a duplicator, this duplicator optically reads information to be duplicated through the transparent layered product. In this case, the transparent layered product is used as a top plate (a document glass on which an original is placed) of the duplicator, and the conductive coating film included in the transparent layered product serves as an antistatic film.
The transparent layered product also can be used as a substrate for a photoelectric conversion device. The photoelectric conversion device includes: a transparent layered product having a glass sheet and a conductive crystalline coating film having a surface with roughness, which is formed on the glass sheet; at least one photoelectric conversion unit; and a back electrode. The surface roughness is caused by crystal grains in the crystalline coating film, and the crystalline coating film includes, at its surface, a transition layer in which the refractive index varies continuously in its thickness direction. The photoelectric conversion unit and the back electrode are stacked in this order on the crystalline coating film. When a variation in the refractive index in the transition layer is shown on a plane defined by a horizontal axis indicating the refractive index and a vertical axis indicating the thickness direction of the transition layer, with the glass sheet positioned on a lower side, the variation in the refractive index is indicated by a convex curve over a whole region of the transition layer.